Lead alloy



1 m in the low PatentedMay 12, 1936' .IUNITED sTATEs PATENT OFFICE a,040,078

mammals Wellington.

No Drawing.

Application November Serial No. 007,144

ilmnanl'. Kaiser,

z Claims. (01. 75-100) ifirantednnderthoactoflifarchs,

This invention relates to an alloy of lead and strontium. It has amongits several objects to produce a compomtion of the type mentioned thatwill have desirable features of mechanical,

6 strength and hardness and resistance to disintegration when subjectedto the action of an electric current while immersed in electrolyte.

Our invention is especially adapted for use in making grids for theplates of storage batteries 10 although its usefulness is by no meanslimited thereto. Usually the grids of both the positive and negativeplates of storage batteries are made of lead to which to of antimony hasbeen added to impart the requisite. strength and hardness. While theeffect of the antimonyis satisfactory in the respects mentioned, it hasa number of disadvantages.

I One such disadvantage is that the composition specified does notfreeze into a homogeneous mass but first segregates crystals of leadwhich, if "un-' disturbed, fall to the bottom of the melt. Finally,

when the proportionof antimony in the still fluid portion of the metalrises to 13%, due to depletion ofthe lead by crystallization, theremainder of additional undesirable feature is that the antimony of thepositive gridis carried, during the "process of charging, into theactivematerial (spongy lead) of the negative electrodes where itproduces local plate.

40 we have found that the alkaline earth meter strontium,.in certainproportiona produee's a de-.

sirable degree of in lead and doesnot have the disadvantages cbnnectedwith the use i of antimony. Itforms an insoluble sulphate and thereforeis ot-P e t inappreciable amounts i in the electrolyte and can not-giverise to local action. v

Useful hardeni V tained by means of this metal whenit is pr s nthardening alloys with lead. By'this is meant that the hardnessisobtained through a special heat treatment the theory of which follows!7 action and sulphation of of the can not be ob-" percentages in whichit forms so id solutions in the lead, but it forms precipitatic ia inlead at a high temperature, near the melting point, than its does atroom temperature. when an alloy having a composition of about thepercentages in which solid solutions are formed is V slowly-cooled toroom temperature the original 5 complete solidification is followed bythe precipitation of minute crystals of an intermetallic compound oflead and the alloying metal within the body of solidified metal. Thecrystals so produced do not add significantly to the hardness of 10 thelead. If, however, the same alloy is quenched suddenly from the hightemperature, the atoms of the alloying metal are trapped in solidsolution but still are not very effective in imparting hardness. If,following this quenching, the lead is allowed to age for several dayseither at room temperature, or perhaps better at a somewhat elevatedtemperature below the melting point, extremely minute and evenlydistributed crystals of the compound are formed which, due to theirsmall size and even distribution, impart a marked degree of strength tothe alloy. For in-. stance, 0.08% of strontium, added to pure lead givesan alloy which after quenching from 300 C. and aging for three weeks at100 C. has a Brinell hardness of from '7 to 9 which is a de sirablehardness for storage battery grids. We have found further that alloy soprepared and treated is not attacked by oxygen .to an appreciablygreater degree than the antimony alloys.

I An alloy of lead containing 0.5% strontium and 0.2% tellurium is veryresistant to intergranular corromon, the presence of the tellurium l atthe grain boundaries rendering these regions 35 more stable. The Brinellhardness of this alloy is .'l.9 both before and after steam corrosion.In addition, the presence of tellurium lowers the sol ubility of gasesin the melted alloy so that a casting is more free from blow holes dueto bubbles o of escaping gas than is acastine made with the alkalineearth metal and lead alone.

, Alloys of lead with 0.04% to 0.20% strontium maybe hardened byquenching from a temperature not far below the freezing point followedby 4.5 aging at e peratures ranging from room temperature tosomewhatbelow the melting point and-are sumciently resistant tocorrosion to be suitable for storage battery grids and while the alloyis largely eutectic has much as 0.5% stronso tium is used, it is stillwell adapted for that use. when tellurium is usedv the percentage ofstrontium may vary between 0.2% and 0.6% and the tellurium between 0.1%-and 0.5%.

the term "balance consisting substantialb purposes, without the paymentof lead is meant that elements other than lead in the portion sodesignated do not substantially exceed 1 per cent 01' the total alloy. 7The invention described herein may be manuiactured and used by or forthe Government of the United States 01' America forv governmentalthereon.

We claim: V 1. An alloy comprising 0.04% to- 0.6% strontium and thebalance co substantially oi 0! any royalties lead, said alloy beingcharacterized by even distribution of minute crystals of the alloy, adesirable degree of hardness, stability at the grain boundaries, lowsolubility of gases when in the molten condition and high resistance tointergranular corrosion and attack by oxygen.

2. An alloy comprising 0.04% to 0.6% strontium, 0.1% to 0.5% telluriumand the rest lead.

